Brakes used in hoisting devices are critical to the operation of the hoisting device both in terms of economy and safety. The malfunction of a brake may lead to dropping the load, whereby other parts of the hoisting device may be damaged and there is a risk that the persons working close by will get hurt.
Brakes used in hoisting devices are conventional disc brakes, in which disc-like friction material rotating along with the motor axle presses against an anchor plate and deceleration takes place.
The friction surface wears during deceleration. If the friction surface wears out, the braking effect of the brake decreases significantly and the brake can no longer operate as designed. Thus, the brake malfunctions.
The condition of a brake is typically monitored manually by measuring the thickness of the friction surface with a slide gauge. So as to be able to measure the friction surface, a possible brake casing thus needs to be dismantled, and after the measurement and the possibly required brake maintenance, the casing needs to be closed again. Brake monitoring thus entails manual labour that is time-consuming and subject to errors. In addition, in hoisting devices, in which the brake is high up, as in harbour cranes, there is a risk that the maintenance person may fall and taking this into account may further add to the time required to perform maintenance.
During the checking of the brake of the hoisting device, the production machine to which the brake is mounted is not available for use for its conventional work. A harbour crane under brake maintenance, for instance, is then out of use during the checking of the brake. However, in terms of economy, the downtime of an expensive apparatus like a harbour crane should be kept as rare and short as possible. Therefore, it is desirable that breaks in the operation of production machines are as short as possible. By scheduling the production breaks, it is possible to shorten the downtime, as the maintenance work can be planned better.
In terms of safety, the wear of a hoisting device brake causes a risk by increasing the probability of the malfunction of the brake, which may cause economic losses, if the hoisting device or its parts break or people in the vicinity of the hoisting device are hurt or damage is caused to the production line or other property. For example, if the brake does not close, the load of the hoisting device may fall. Also, if the brake does not close, the motor of the hoisting device may run against the brake and the brake may overheat and even explode.